Manufacture of artificial silk



Patented se i. 29,1942

um 'rso f ST TE VEFPAIE .OFFICE. f

. Manor-across or aarmcmnsna I JohannJosephStoeckly, Teltow, andWolfgang Linnhofl, Berlin-M171 Alien Proper y (3!" Noni-swin assu es-my,1939, semi No.

the

tRGcrmany;vestedin 272,834. In Germany Mayll, 1938 V 4, Claims. It isalready Well known to spin viscose solutions into a conventional,primary, acid spin bath containing various salts, and to stretchthethreads, thus obtained, in a hot secondary bath. British Patent#467,500, for example, discloses the beneficial eil'ect of the primary-spinfbath upon the ultimate physical characteristics of i. e.,bathscontaining 4% of zinc sulphate spun viscose threads, and itrecommends the -use-- of primary spin baths with a high zinc content,

(about 50 g. of ZnSOrper' liter of bath); Ac- 1 cording to-this process,it is possible to produce a 120 den. thread with 60 filaments in a warmspin bath containing about 9.5% of sulphuric acid, 20% ofsodium'sulphate and 4% of zincsulphate and to stretch the thread 87%after a bath travel of about 20 'cm. in said primary bath acid contentofthe. primary bath'cause's a reduction of its coagulating and/orprecipitating flciency by adding other suitable ingredients thereto.Thus, we have found that the zinc sulphate and sulphuric acid content ofthe priin a secondary bath maintained at a temperature or at least 60 C.and preferably of about 95 0., this secondary bath containing only smallquantities of the bath ingredients present inthe' primary bath. The highzinc content of the primary bath is evidently responsible for the goodphysical properties of viscosethreads pro:

duced therein. However, it has .been found in actual practice that spinbaths having a high zinc content cause rapid clogging of spinneret'orifices through which the viscose solution is extruded into such baths.

It is, therefore, a-primary object of our invention to provide azinc-bearing spin bath..

which substantially prevents the clogging of spinneret orifices withoutreducing the physical characteristics of viscose threads formed thereinin comparison in the art.

with spin baths heretofore known Other objects of our invention willbecome apparent to those skilled in the art from of the followingspecification.

Many theories have been advanced to explain therole'which zinc sulphateand other soluble zinc. salts play in.the aforementioned spinning astudyprocesses. It has been saidthat the favorable lesultsobtained with zincsulphate-are due to its retarding eifect upon the decomposition of 5'the thread at the beginning of the stretching step. However, ourexperiments have shown that this retarding eitect of zinc sulphatecannotfully explain the beneficial results obtained therewith sinceammoniumsulphate baths, as is well known, neither cause the formation of a. de-

thread nor a favorable result. 2 For thisreasomitis 'topresumethatzincsulphate causes very specific eirects besides retarding the and/ordecomposition of.

viscose threads. It is very likely that the zinc viscose (xanthate)formed in the primary spin bath causes a retardation of the finaldecomposition of the thread and that the thread and/or this compoundought not be completely decomposed upon entering the fixing and/orstretching bath.- The ;rate of decomposition ofjthis intermediate.compound is however, as our experiments showed, only retarded when thesulphuric acid concentration of the primary spin bathis reduced andpreferably. brought to a minimum. Sinceareductioh of the sulphuricpower, it is necessary tocompensate for this demary bath my be reducedprovided larger amountsof magnesium sulphate'are added thereto.Additions of 150 g.,' 200 g., 250 g. and

more of magnesium sulphate per liter of spin bath have given excellentresults.' Instead of using a primary'bath containing 125 g. of sulphuricacid, 260 g. of sodium sulphate and 52 g.

of zinc sulphate per liter,'it'is possible to use spin bath's havingthe'following compositions:

Sulphuric Sodium fl Zinc a id, sulphate Bath um Gram P,"

m an. m0

' 'Ihesenovel spin baths substantially inhibit clogging of spinneretorifices. This is especially true when the zinc sulphate content isreduced to about 30 grams .per liter of bath,- or below this value. Thestretchability of threads is at least equalto that main -baths having ahigher zinc content while the physical characteristics of'the finishedthreads are maintained. This reical which reduces the stretchability ofviscose threads spun in its presence. Indeed, further experiments haveproven that magnesium sulphate is not capable of completely replacingzinc sulphate in primary'spin baths. For this reason *1 w sulphate makesit and tocause indirectly a-retardation of.the decomposition of viscose.For this reason it issulpbate suit is-entirely unexpected sincemagnesium sulphate has heretofore been regarded as a .chemalso possibleto reduce the zincsulphate concentratlons of the primary spin baths.

We claim:

1. The process of producing threads of regenerated cellulose whichcomprises first spinning a viscose solution through the orifices of aspinneret into a primary, zinc-bearing, aqueous spin bath to form anincompletely decomposed viscose thread therein and subsequentlystretching and decomposing said thread in a hot, secondary, aqueous spinbath to form a threadof regenerated cellulose, said primary spin bathcontaining about 16 to 30 grams of zinc sulphate, about 110 to 115 gramsof sulphuric acid, about 150 to 250 grams of magnesium sulphate andabout 200 to 260 grams of sodium sulphate per liter of bath, and saidsecondary spin bath having a temperature of at least 60 C. andcontaining less sodium sulphate, zinc sulphate, sulphuric acid andmagnesium sulphate per liter of bath than said priand decomposing saidthread in a hot, secondary,

aqueous spin bath to form a thread of regenerated cellulose, saidprimary spin bath containing about 200 grams of sodium sulphate, about20 Y grams of zinc sulphate, about 115 grams of sulmary bath, wherebyincrustation of said spinneret is substantially prevented. a

2. The process of producing threads of regenerated cellulose whichcomprises first spinning a viscose solution through the orifices of aspinneret into-a primary, zinc-bearing, aqueous spin bath to form anincompletely decomposed viscose thread therein and subsequentlystretching and decomposing said thread in a hot, secondary, aqueous spinbath to form a thread of regenerated cellulose, said primary spin bathcontaining about 260 grams of sodium sulphate, about 30 grams of zincsulphate, about 115 grams of sulphuric acid and about 200 grams ofmagnesium sulphate per liter of spin bath, and said secondary spin bathhaving a temperature of at least 60 C. and containing less sodiumsulphate, zinc sulphate, sulphuric acid and magnesium sulphate per literof bath than said primary bath, whereby incrustation of said spinneretis substantially prevented.

phuric acid and about 250 grams of magnesium sulphate per liter of spinbath, and said secondary spin bath having a temperature of at least 60C. and-containing less sodium sulphate, zinc sulphate, sulphuric acidand magnesium sulphate per liter of bath than said primary bath, wherebyincrustation of said spinneret is substantially prevented.

4. The process of producing threads of regenerated cellulose whichcomprises first spinning a viscose solution through the orifices of aspinneret into a-primary, zinc-bearing, aqueous spin bath to form anincompletely decomposed viscose thread therein and subsequentlystretching and decomposing said thread in a hot, secondary,-

p by incrustation of said spinneret is substantially

